1. Field of the Invention
The present invention relates to a fuel injection apparatus for injecting fuel in an intake port of an internal combustion engine, particularly to the rear surface of an intake valve.
2. Description of the Related Art
FIGS. 3 and 4 show a related art for comparison with the present invention. In these figures, 1 is an intake valve, 2 is a stem of the intake valve, and 3 is a valve face of the intake valve. The valve face 3 forms a conical surface and is polished. Reference numeral 4 shows an end portion (intake port) of an intake port. A fuel injector 5 is attached to this so that its injection port 6 is brought close to a depression formed at a part of the same. As clear from FIG. 3 and FIG. 4, in the past, the part A of the umbrella portion comprised of a curved surface of a surface of revolution formed at the rear surface of the intake valve 1 is used as the "spray target position" and the fuel injector 5 and the direction of the injection port 6 of the same are set so that the fuel spray injected from the fuel injector 5 heads toward the position A and strikes the front surface of the same perpendicularly. Note that 7 is the center line of the fuel spray and that 8 is a throttle valve provided at an upstream portion of the intake port 4.
In a conventional fuel injection apparatus as mentioned above, the "spray target position" is set to a portion such as A on the umbrella portion 1a of the intake valve, so the angle of incidence of the center line 7 of the fuel spray with respect to the normal line at the position A becomes approximately 0 and the angle .theta. of the center line 7 of the fuel spray intersecting with the surface of the umbrella portion 1a becomes about 90 degrees as shown in FIG. 4. That is, the center line 7 of the fuel spray substantially coincides with the normal line at the position A. Therefore, the fuel spray striking the position A of the intake valve 1 deposits at the rear surface of the intake valve 1, including the part of the umbrella portion 1a, as shown as W in FIG. 3 and FIG. 4, and then spreads to its surroundings. Part of the fuel spray also sprays and deposits on the inner surface of the intake port 4. The fuel deposited on these surfaces forms liquid films on these surfaces.
Even if the intake valve 1 opens and a flow of intake air occurs in the intake port 4, the flow rate of the intake air in the vicinity of the umbrella portion 1a and on the inner surface of the intake port 4 is relatively low, so part of the fuel depositing on the umbrella portion 1a etc. and forming the liquid film evaporates slowly and remains in the intake port 4 unevaporated. The fuel of the portion other than that remaining as a liquid film in the intake port 4 flows down to part of the valve face 3 and flows into the combustion chamber of the engine when the intake valve 1 opens, but at the time of engine startup or cold acceleration etc. when the amount of injection becomes larger, fuel builds up in a narrow range of about one-third of the valve face 3, so the fuel becomes a liquid film even when flowing from the opened intake valve 1 to the combustion chamber.
In the conventional fuel injection apparatus, a liquid film is formed in a relatively broad area in the intake port 4 in this way, so the entire amount of the fuel injected from the fuel injector 5 is not supplied immediately inside the combustion chamber of the engine. This causes a reduction in the response to fuel injection control. Further, depending on the operating state of the engine, even the fuel flowing into the combustion chamber becomes a liquid film, so the state of vaporization of the fuel in the combustion chamber becomes incomplete and the state of combustion deteriorates. Accordingly, poor startup, rough acceleration, or other undesirable states occur due to these factors, the liquid film of the fuel remaining deposited on the intake port 4 evaporates at the time of deceleration and causes the air-fuel ratio in the combustion chamber to become overly rich, and therefore an increase in emission of HC and CO in the exhaust may result.